The overall goal of the proposed research is to gain deeper insight into the mechanism of action of trimethylamine dehydrogenase (TMADH), a member of an important group of enzymes that contain multiple redox-active centers and which have overall catalytic mechanisms involving electron transfer between these sites. In addition to their physiological significance, these proteins serve as extremely useful systems in which to examine the factors which govern the magnetic and electron-transfer interactions between such centers. The reaction catalyzed by TMADH, the oxidative demethylation of trimethylamine to dimethylamine and formaldehyde, is of considerable intrinsic interest in understanding the chemistry available to the isoalloxazine ring in biological systems. This chemistry is relevant to a number of other enzymes, including such clinically important enzymes as monoamine oxidase. The proposed work builds on previous work by the PI and has the following principal objectives: Examination of the role of specific amino acid residues in the reaction catalyzed by TMADH; characterization of the reaction of TMADH using time-resolved crystallography; characterization of the unusually strong magnetic interaction between the flavin and Fe4S4 semiquinone centers of TMADH; examination of the electrochemical and electron-transferring properties of TMADH; and characterization of the interaction between trimethylamine dehydrogenase and its physiological electron acceptor, and electron-transferring flavoprotein. Guided by the three-dimensional structure of trimethylamine dehydrogenase, the roles of specific amino acid residues in the active site of the enzyme with regard to each of these areas will be addressed by site-directed mutagenesis. The intention of this work is to construct a comprehensive picture of the relationship of structure to function in trimethylamine dehydrogenase that furthers our basic understanding of the mechanism of this and related enzymes.